1. Field of the Invention
This invention relates to a differential pressure forming machine which differentially pressure forms articles in a sheet of thermoplastic material and more particularly to method and apparatus for trimming articles from a thermoplastic sheet utilizing trim dies which are moved by a wedge that is driven by a servomotor driven crank in a to-and-fro path of travel transverse to the path of travel of the trim dies.
2. Description of the Prior Art and Objects
Apparatus, such as that disclosed in U.S. Pat. No. 3,664,791 granted to G. W. Brown on May 23, 1972, which is incorporated herein by reference, has been provided heretofore for successively delivering a heated thermoplastic sheet to a heating station and then to a forming station at which molds engage the sheet to differentially pressure form an article in the sheet.
Apparatus such as that disclosed in U.S. Pat. No. 4,313,358, granted to Gaylord W. Brown on Feb. 2, 1982, which is incorporated herein by reference, has been provided heretofore for trimming articles, differentially pressure formed in a thermoplastic sheet, at a trimming station which is downstream of the forming station.
In this latter mentioned patent, the trim dies are actuated through toggle linkages and cams which move the trim dies to positions engaging opposite sides of the sheet and thence to sheet severing positions.
The trim dies provided in the prior art differential pressure forming machines are actuated by direct acting, pneumatically operated cylinders and/or cams for moving the trim mechanism to sever the differentially pressure formed article from the sheet.
Because of the rather substantial force required to move the trim dies between spaced apart, open positions, and closed positions, the prior art utilized double acting pneumatically operated cylinders which are quite large and relatively expensive. It has been found advantageous to utilize a wedge which is moveable transversely to the path of a movement of the trim dies for moving the trim dies from the open positions to the closed positions. Accordingly, it is an object of the present invention to provide a new and novel trim die machine including trim dies which are moveable in to-and-for longitudinal paths of travel and wedge mechanism, which is transversely moveable for wedging the trim dies between open positions and closed positions engaging opposite sides of the sheet.
U.S. Pat. No. 5,225,213 issued to G. W. Brown and Albert W. Arends on Jul. 6, 1993, discloses apparatus for trimming an article from a thermoplastic material including a wedge for incrementally moving the trim die from a closed position, in which the dies engage opposite sides of the sheet, to a further closed position in which the trim dies sever the sheet. This prior art wedge is also transversely moved via a pneumatically operated cylinder which is relatively expensive and inefficient. Accordingly, it is another object of the present invention to provide a new and novel trim machine including a transversely moveable wedge which is operated via a motor driven crank and which is more efficient than the pneumatically operated cylinders utilized heretofore.
The positioning of prior art pneumatically driven wedge is also relatively difficult to control and thus, the exact starting and stopping positions of the wedge, and the resultant distance which the molds move, is sometimes less accurate than desired. Accordingly, it is another object of the present invention to provide a new and novel trim machine of the type described which includes new and novel servomotor drive mechanism for more accurately controlling the starting and stopping positions of a wedge for moving the trim dies.
Another object of the present invention is to provide a trim machine of the type described which includes mechanism for electronically adjusting the stroke of the trim die by starting and stopping a servomotor which drives the trim die moving wedge in any selected one of a plurality of different positions.
It is sometimes desirable to move the trim platen a significant distance vertically at a rapid distance between the open positions and the closed, sheet engaging positions and the wedge disclosed in the aforementioned U.S. Pat. No. 5,225,213 did not provide structure for this to be accomplished. Accordingly, it is another object of the present invention to provide new and novel trim apparatus of the type described which includes new and novel wedge mechanism for moving the trim dies at varying rates of travel.
It has been found advantageous to not only utilize a wedge for moving the trim dies between the closed positions and the sheet severing positions but also to move the trim dies from the open positions to the closed positions. Accordingly, it is another object of the present invention to provide a new and novel trim machine including a new and novel motor driven wedge for moving the platen between the removed positions and closed positions.
It is a further object of the present invention to provide a new and novel trim machine of the type described which includes a first wedge section having a first inclination for relatively rapidly moving the trim dies between the open positions and the closed positions and a second wedge portion having a second lesser inclination for more slowly moving the trim dies between the closed positions and the sheet severing positions at a substantially lesser rate.
It is a still further object of the present invention to provide a new and novel trim machine of the type described having a first transversely moveable wedge portion for moving the trim dies from spaced apart positions to closed positions engaging opposite sides of the sheet and a second wedge for incrementally further moving the trim dies to sheet severing positions.
It is still a further object of the present invention to provide a trim machine of the type described including wedge mechanism for moving the trim dies between open, spaced apart positions to closed, sheet engaging positions at a first rate of travel and moving the trim dies from the closed positions to further closed, sheet severing positions at a lesser rate of travel.
The power required to relatively move the trim dies together is substantially greater when the trim dies are moving from the closed positions to the severing positions than when moving from the open positions to the closed positions. Accordingly, the degree of inclination of the wedge portion utilized to move the trim dies from the closed position to the sheet severing position must be substantially less than the degree of inclination of the wedge utilized to move the trim dies between the open positions and the closed positions when the trim dies are not operating in a cutting or severing mode. Accordingly, it has been discovered advantageous, according to the present invention, to provide a trim die moving wedge which incorporates a two step wedge having a first wedge section with a relatively sharp inclination for rapidly, relatively moving the non-loaded trim die and a section wedge section with a relatively lesser inclination for less rapidly relatively moving the die, while under load.
Accordingly, it is another object of the present invention to provide a trim machine of the type described which includes a two stage wedge having a first wedge portion with a sharp inclined cam surface for rapidly moving the trim die when the trim die is not under cutting load and a second wedge cam surface of substantially lesser inclination for moving the trim die while it is under cutting load.
Another object of the present invention is to provide a method for trimming an article from a thermoplastic sheet via new and novel wedge mechanism which more accurately controls the stroke of travel of the trim dies.
Another object of the present invention is to provide a method of trimming articles from a thermoplastic sheet of the type described including the step of converting rotary motion to linear motion via a crank which is swung in opposite directions of travel to any selected one of a plurality of degrees of travel to selectively control the stroke of the trim die to any selected one of a plurality of different trim strokes.
Other objects and advantages of the present invention will become apparent to those of ordinary skill in the art as the description thereof proceeds.